The present invention relates to a vaporized fuel control apparatus for an internal combustion engine, which is designed so that fuel vapor formed in the fuel tank is recovered and delivered to the intake system of the engine.
Apparatuses of this type are known in the art in which the fuel vapor generated in the fuel tank is adsorbed to a canister so that when the engine is running, the fuel vapor is suitably discharged into the intake system of the engine and burned in the combustion chamber of the engine, thereby preventing the emission of the fuel vapor in the fuel tank directly into the atmosphere (e.g., Japanese Unexamined Publication No. 61-19962).
Then, the recent trend has been toward strengthening the regulations on the automotive exhaust emission control and there has also been a movement toward limiting the amount of fuel vapor escaping from the fuel filler port during the refuelling period and preventing the pollution of the atmosphere. However, there is a disadvantage that the amount of fuel vapor formed during the refuelling period is so large that when the fuel vapor is first adsorbed to the canister and then discharged into the intake system of the engine, the air-fuel ratio of the mixture supplied to the engine is decreased considerably (enriched) so that not only the CO and HC constituents in the exhaust gases by the combustion are increased but also the operating performance of the engine is deteriorated.